1. Technical Field
The present invention relates to a composition for photoresist development and a method of developing a photoresist using the same.
2. Description of the Related Art
When a semiconductor or the like is mounted on a printed circuit board, a process of developing a photoresist layer is followed. Such a developing process means a process of removing a photoresist layer. The photoresist layer serves as an insulation layer or protective layer of a printed circuit board. A solder resist is included in a photoresist. Such a photoresist developing process is known as a solder resist opening process. Such a solder resist opening process is necessarily required in order to secure a passage for electrical connection between a chip mounted on a printed circuit board and a wiring layer formed on the printed circuit board.
As a conventional photoresist opening method, buffing, plasma etching, chemical etching or the like is known. Buffing or plasma etching is a method of forming a photoresist layer having a thickness equal to or less than the height of a copper pattern by curing a photoresist and then physically or chemicophysically treating the cured photoresist. Chemical etching is a method of forming a photoresist layer having a thickness equal to or less than the height of a copper pattern by treating the unexposed area (uncured area) of a photoresist with a chemical. The chemical used in a conventional developing method is an aqueous alkali solution. Meanwhile, most conventional developing solutions are prepared using a salt containing a monovalent cation. Particularly, as disclosed in the following Patent document 1, an aqueous solution containing 1 wt % of sodium carbonate (Na2CO3) is used as a developing solution.
Meanwhile, recently, three-dimensional packaging technologies have attracted considerable attention in relation to the provision of various circuit patterns and mounting conditions. In order to use such three-dimensional technologies, a photoresist must be provided with predetermined bumps, and, in order to secure such bumps, precisely-controllable developing technologies are required during a photoresist developing process. For this purpose, conventionally, a partial curing process has been used. However, this partial curing process is problematic in that it is difficult to secure precise bumps and control the developing depth of a photoresist because of the characteristics of developing chemicals used in this process.
As a conventional technology for controlling the developing depth of a photoresist, a method of diluting a developing chemical with water, a method of controlling developing time, or the like, has been used. Here, the developing chemical is an aqueous solution containing a salt having a monovalent cation. The development principle of a conventional developing solution including an aqueous solution containing a salt having a monovalent cation is realized by a process in which sodium (Na) included in the developing solution reacts with a carboxyl group (—COOH) included in a photoresist to obtain —COONa, thus saponifying the photoresist to melt the photoresist. However, due to the characteristics of —COONa, which is hydrophilic, —COONa is rapidly detached from the photoresist by water (H2O) existing therearound, and thus it becomes difficult to control the developing speed of a photoresist. Meanwhile, even when the developing depth of a photoresist is controlled to some degree by diluting a convention developing solution, there remains a problem in that the developed surface of a photoresist is very irregular, and thus a spatial environment for precise three-dimensional packaging cannot be provided.
Patent document 1: Japanese Unexamined Patent Application Publication No. 2011-192692